DISCHARGE VALVE ACTUATING SYSTEM FOR HERMETIC COMPRESSORS

Abstract: Discharge valve actuating system for hermetic compressors, of the type comprising: a piston (3) reciprocating inside a cylinder (2), which pumps gas to a discharge chamber (22), maintained in selective fluid communication with the cylinder (2) through a discharge orifice (12) provided on a valve plate (10) and closed by a respective reed discharge valve (40), said system comprising at least one subchamber (70), which maintains with the discharge chamber (22) a fluid communication that is constantly blocked by a movable blocking element (60), which moves between an operative position of contact with the discharge valve (40) when at a closed position and an inoperative position of spacing from said discharge valve (40), said inoperative and operative positions being defined in function of the pressure inside the discharge chamber (22) in relation to that pressure existing in the subchamber (70) during each pumping cycle of the piston (3).

Description: DISCHARGE VALVE ACTUATING SYSTEM FOR HERMETIC COMPRESSORS Field of the Invention The present invention refers to a discharge valve actuating system for reciprocating hermetic compressors, which are used in small refrigerating appliances and which are provided with a discharge valve having an impelling means. Background of the Invention Reciprocating hermetic compressors of refrigeration are provided with a block, which is mounted inside a hermetically sealed shell. In said block, there is defined a cylinder, in which reciprocates a piston, which is driven by the shaft of an electric motor through a connecting rod, in order to effect the suction and compression of a refrigerant gas. The cylinder presents an end, which is opposite to that end by which the piston is articulated to the connecting rod, and which is opened to a valve plate, which separates the internal cavity of said cylinder from a cylinder head, where the discharge and suction chambers of the compressor are defined. The communication between the internal cavity of the cylinder and each of said chambers is made through discharge and suction orifices provided on said valve plate, which are periodically and selectively closed by respective discharge and suction valves, mounted on said valve plate. For reasons of constructive simplicity, these compressors use suction and discharge valves of the reed type, which, together with the piston, produce an intermittent flow of refrigerant gas. These systems further present muffler assemblies or acoustic filters, mounted at the suction and discharge lines of the compressor, in order to attenuate the noises caused by said intermittent flow of refrigerant gas. Such muffler assemblies include at least one discharge muffler, where the compressed gas coming from the compressor is expanded, reducing its pressure and, consequently, reducing the noise intensity. The known discharge mufflers are usually defined by a chamber, which is formed in the cast block of the cylinder and which has a first channel, communicating with the discharge chamber, and a second channel, communicating with the discharge tube or, in some constructions, with a second discharge muffler chamber. It is known that during the discharge of the refrigerant gas to the discharge chamber, the hermetic compressors present yield loss, resulting from the late opening of the discharge valve. This means that the discharge valve is opened at an instant of time posterior to the instant in which the discharge pressure is achieved, i.e., the pressure inside the cylinder at compression end has surpassed that minimum pressure needed to cause the opening of the discharge valve. This late opening results from inertial problems of the valve movement, due to its constructive characteristics, or from a glueing effect of the contact surface of said discharge valve with an oil film existing on the valve seat. A solution to eliminate the problem of opening delay of the discharge valve during compression is by using a valve impelling means, which actuates together with said discharge valve, as described in the Brazilian patent document PI9002967. Nevertheless, as in this solution the valve impelling means is constantly actuating together with the discharge valve, forcing the latter to open, the closing of said valve is impaired. This constant actuation of the impelling means allows a gas backflow to the cylinder inside, with a consequent volumetric loss for the compressor. Disclosure of the Invention Thus, it is a general object of the present invention to provide a discharge valve actuating system for reciprocating hermetic compressors, which minimizes the effect of the forces actuating on the discharge valve that delay its opening during compression, thereby increasing the compressor yield, without impairing the closing of said discharge valve. It is a more specific object of the present invention to provide a discharge valve actuating system for reciprocating hermetic compressors of the above cited type, which minimizes the effect of the forces that delay the opening of said valve, by using the power available in the compressor. These and other objectives are achieved by a discharge valve actuating system for reciprocating hermetic compressors, of the type comprising: a piston reciprocating inside a cylinder; a valve plate, closing a pumping end of the cylinder; and a cylinder head, attached to the valve plate, in order to define with the latter a discharge chamber, which is maintained in selective fluid communication with the cylinder through a discharge orifice, which is provided on the valve plate and which is closed by a respective reed discharge valve, and further comprising: at least one subchamber, which maintains with the discharge chamber a fluid communication that is constantly blocked by a movable blocking element, which moves between an operative position, defined when the pressure in the discharge chamber and in the subchamber are substantially the same, and an inoperative position, displaced towards the subchamber and achieved whenever the pressure inside the discharge chamber surpasses the pressure of the subchamber, by a value sufficient to cause said displacement of the blocking element from the inoperative position to the operative position, the blocking element being constantly and elastically forced to the operative position, in which said blocking element applies on the discharge valve a force to move the latter from its closed position to a position spaced from the discharge orifice. Brief Description of the Drawings The invention will be described below, with reference to the attached drawings, in which: Fig. 1 is a partial horizontal sectional view of the cylinder block of a prior art compressor, illustrating the cylinder and the gas suction and discharge chambers, formed between the cylinder head and the valve plate,* and Fig. 2 illustrates, rather schematically, a partial horizontal sectional view of details of part of figure 1, showing the discharge chamber and the discharge muffler chamber in a compressor provided with the valve actuating system of the present invention. Best Mode of Carrying Out the Invention According to figures 1 and 2, the reciprocating hermetic compressor used in the present invention comprises a cylinder block 1, where is defined a cylinder 2, in which inside reciprocates a piston 3, driven by a connecting rod 4. The cylinder block 1 presents a pair of opposite faces, to which are opened the ends of the cylinder 2, a valve plate 10 and a cylinder head 20 being attached against one of said opposite faces of the cylinder 1, the cylinder head 20 forming together with said valve plate 10 two internal cavities, one of which defining a suction chamber 21 and the other defining a discharge chamber 22. The cylinder 2 maintains a selective fluid communication with said suction chamber 21 and discharge chamber 22, throuth respective gas suction and discharge orifices 11 and 12, provided on the valve plate 10, in which are mounted respective suction valve 30 and discharge valve 40, both of the reed type and actuating during the suction and discharge strokes of the operative cycle of the reciprocating piston 3. Each said valve, when at the closed condition, presents a sealing portion seated on a corresponding valve seat 11a, 12a, defined at an adjacent portion of the respective orifice of the valve plate 10, the discharge valve 40 being mounted against a front face 10a of the valve plate 10 facing the inside of the discharge chamber 22. In the known compressors, the opening of the discharge valve 40, even when it is a valve with an impelling means such as described in the Brazilian patent application PI9002967 of the same applicant, is obtained when the pressure inside the cylinder 2, together with the force of the impelling means (if there is one) , results in an opening force upstream said discharge valve 40, corresponding to the summing of the retarding forces acting on said discharge valve 40, in order to keep the latter seated on the respective valve seat 12a. Nevertheless, the action of this opening force can only overcome the retarding forces at an instant of time posterior to the instant in which the pressure in the cylinder 2 reaches its discharge value. Moreover, the compressors in which there is an impelling means to minimize this time difference, present the inconvenience of having said impelling means in permanent activity, thereby impairing the closing of the discharge valve 40. These retarding forces include inertia of movement of said discharge valve 40 and an effect of adhesion of the latter to the corresponding valve seat 12a, caused by the presence of an oil film between one portion of the lower face of the discharge valve 40 facing the valve plate 10 and said valve seat 12a of said discharge valve 40. The valve plate 10 presents, at its front face 10a, a lowered portion 13, which is provided adjacent to the discharge orifice 12 and which lodges therewithin a pneumatic valve impelling means 60, disposed in such a way as to actuate against the face of the discharge valve 40 facing the valve plate 10, in order to cause the opening of said discharge valve 40, at least at the final phase of the compression stroke, said actuation beginning after a certain time of the compression end has elapsed, as described below. The impelling means 60 defines, between the discharge chamber 22 and said lowered portion 13, a subchamber 70, adjacent to the discharge chamber 22 and separated therefrom by a movable blocking element or wall, in order to avoid any direct fluid communication with said discharge chamber 22 through the lowered portion 13. A constant fluid communication with the discharge chamber 22 occurs through an intermediate connecting volume 80, through which the compression gas flows before reaching the subchamber 70. In the illustrated construction, said intermediate connecting volume 80 is defined by a discharge muffler chamber, provided in the cylinder block 1. The impelling means 60 presents an operative position, defined when the pressure in the discharge chamber 22 substantially equals the pressure in the subchamber 70, and an inoperative position, displaced towards the subchamber when the pressure in the discharge chamber 22 is higher than that of the subchamber 70, said impelling means being maintained constantly elastically in this condition, while there is a pressure differential between the discharge chamber 22 and the subchamber 70. In the operative position, the impelling means 60 keeps contact with the discharge valve 40 at least at one point of the latter. In the preferred illustrated form, said contact is unique, the valve impelling means 60 being designed in such a way as to exert an opening force against the discharge valve 40, without causing torsions on the latter around is longitudinal axis . The use of an intermediate volume 80 prevents the pressure variations in the discharge chamber 22 from being transmitted to the subchamber 70, thus avoiding to submit the impelling means 60, and consequently the discharge valve 40, to an opening force before the programmed opening instant, thereby impairing the adequate closing of the discharge valve 40. Moreover, said intermediate volume 80 is constructed in such a way that the compression gas, propagating to the subchamber 70, reaches the latter within a time posterior to the closing of the discharge valve 40, without affecting said closing and in time to cause a new operative condition of the valve impelling means 60, before a new discharge pressure is reached in the cylinder 2. The operative condition of the valve impelling means 60 is associated with a condition of pressure balance between the subchamber 70 and the discharge chamber 22, established after a determined time interval for the closing of the discharge valve 40 has elapsed, said balance actuating in the impelling means 60 till the instant of a new opening of the discharge valve. In the illustrated construction, the valve impelling means 60 comprises a separating element 61, such as a flexible pneumatic membrane, carrying a valve actuating means 62, said flexible membrane being mounted in the lowered portion 13, separating the subchamber 70 from the discharge chamber 22 and avoiding the fluid communication therebetween. In this construction, it is possible to provide the subchamber 70 with a protecting stop, which acts against the impelling means 60, so as to limit the retracting displacement of the latter and, consequently, its bending, to a deformation at maximum slightly higher than that needed to obtain and maintain the spacing between the valve actuating means 62 and the discharge valve 40, upon the sudden pressure rise in the discharge chamber 22 during the opening of said discharge valve 40. The valve actuating means 62 is in the form of a pneumatic valve actuating means, projecting from the flexible membrane 61 and having a connecting end through which said valve actuating means 62 is attached to said flexible membrane 61, and an opposite free end, which is in contact with an adjacent portion of the discharge valve 40, when the latter is at its closed position and the valve actuating means 62 is at an operative condition, achieved by the pressure balance between the discharge chamber 22 and subchamber 70. In this operative condition, the valve actuating means 62 remains temporarily forcing the discharge valve 40 to a partial opening condition, when said discharge valve 40 is not subjected to the retarding forces acting thereon and is maintained adhered to the respective valve seat 12a, till the opening of said valve. In the illustrated construction, the communication between the discharge muffler chamber 80 and the discharge chamber 22 is made through a first gas conducting tube 81, which is opened to the inside of the discharge chamber 22, by means of a throughbore 23 provided in the body of the cylinder head 20, transversely to the wall adjacent to the discharge muffler chamber 80. The communication between the latter and the subchamber 70 is made through a second gas conducting tube 82, having one end mounted in the discharge muffler chamber 80 and an opposite end connected to a first end of a through channel 24, provided along a portion of the valve plate 10, the second end of said channel, opposite to the first end, being opened to the subchamber 70. According to the present invention, when the pressure inside the cylinder 2 reaches the discharge pressure, the discharge valve 40 opens instantaneously, allowing the gas compressed inside the cylinder 2 to reach the discharge chamber 22, by passing through the discharge orifice 12. This opening is due to the action of the valve impelling means 60 on said discharge valve 40, liberating said valve from the action of the retarding forces and forcing it to the partial opening position, as described above. The opening of the discharge valve 40 generates a temporary pressure rise in the discharge chamber 22, causing a pressure unbalance between the latter and the subchamber 70. This pressure rise in the discharge chamber 22 forces the impelling means 60 to a retracting inoperative position, when said impelling means is separated from the adjacent portion of the discharge valve 40, said inoperative position lasting till the pressure in the subchamber 70 equals the pressure in the discharge chamber 22 and again causes the operative position of the valve actuating means 62. This separation may occur by the individual retraction of the flexible membrane 61, as well as of the valve actuating means 62, in case both are sensible to the pressure variations between the discharge chamber 22 and subchamber 70. The retracting condition of the impelling means 60 will last as much as the pressure unbalance between the discharge chamber 22 and subchamber 70. This unbalance lasts till after the closing condition of the discharge valve 40 is reached. The time to return to the balance condition and consequently, to the operative position of the valve actuating means 62, is calculated so that said condition be reached before a new condition of discharge pressure inside the cylinder. The return time to the pressure balance condition corresponds to the time the compressed gas takes to flow from the discharge chamber 22 to the subchamber 70, which means the time needed by said gas to pass through the intermediate volume 80 or, according to the preferred illustrated form, through the discharge muffler chamber 80. The balance condition may occur at any instant of time after the closing of the discharge valve 40. According to the present invention, the balance condition is achieved at a time close to that in which a new condition of gas discharge pressure in the cylinder is reached, in order to avoid that possible oscilations that by chance were not attenuated in the intermediate volume be transmitted to the valve impelling means 60, leading the discharge valve 40 to an early inadequate partial opening condition. The valve actuating means 62 may also be in the form of a stiff element, such as an impelling needle, which maintains a selective contact with the adjacent sealing portion of the discharge valve 40. In the opening of the latter, the higher pressure in the discharge chamber 22 exerts a force on the flexible membrane 61, in the direction of retraction thereof relatively to the discharge valve 40. This force results in the retraction of said impelling needle, avoiding any contact with the discharge valve 40, even when the latter is in the closed condition. In another embodiment of the invention (not illustrated) , the impelling needle or stem is mounted to a flexible membrane, such as described above, attached to a receiving recess, provided on the internal wall of the cylinder head 20 and opposite to the valve plate 10, so that the free end of said impelling needle keeps contact with a portion of the upper face of the discharge valve 40, opposite to the sealing portion of the latter. Though not illustrated, other constructions are also possible, in which the actuation of the discharge valve 40 is made by more than one impelling means mounted in subchambers 70. Moreover, at least one of said subchambers 70 may be defined spaced from or adjacent to the cylinder head. These solutions further include the possibility of the subchambers 70 being hermetic, defining chambers of predetermined constant pressure. Either one of said constructions permits to achieve a valve opening at an instant of time closer to the instant in which the discharge pressure is reached inside the cylinder 2, without however affecting or even altering the closing of said discharge valve 40 during the operative cycle of the reciprocating piston 3. Though the above description refers to constructions directed only to the discharge valve of the hermetic compressor, said solutions may also be applied to the suction valve.

Claims: CLAIMS 1. Discharge valve actuating system for hermetic compressors, of the type comprising: a piston (3) reciprocating inside a cylinder (2) ,* a valve plate (10) , closing a pumping end of the cylinder (2) ; and a cylinder head (20) , attached to the valve plate (10) , in order to define with the latter a discharge chamber (22), which is maintained in selective fluid communication with the cylinder (2) through a discharge orifice (12), which is provided on the valve plate (10) and which is closed by a respective reed discharge valve (40), characterized in that it comprises: at least one subchamber (70) , which maintains with the discharge chamber (22) a fluid communication that is constantly blocked by a movable blocking element (60) , which is moved between an operative position, defined when the pressure in the discharge chamber (22) and in the subchamber (70) are substantially the same, and an inoperative position, displaced towards the subchamber (70) and achieved whenever the pressure inside the discharge chamber (22) surpasses the pressure of the subchamber (70) , by a value sufficient to cause said displacement of the blocking element (60) from the inoperative position to the operative position, the blocking element (60) being constantly and elastically forced to the operative position, in which said blocking element (60) applies on the discharge valve (40) a force to move the latter from its closed position to a position spaced from the discharge orifice (12) . 2. Discharge valve actuating system, as in claim 1, characterized in that at least one subchamber (70) is adjacent to the discharge chamber (22) . 3. Discharge valve actuating system, as in claim 2, characterized in that each subchamber (70) is defined in a respective lowered portion (13) provided in one of the internal walls of the discharge chamber (22) . 4. Discharge valve actuating system, as in claim 3, characterized in that the lowered portion (13) is provided on the valve plate (10) at a portion thereof adjacent to the discharge orifice (12) . 5. Discharge valve actuating system, as in claim 1, characterized in that the blocking element (60) keeps contact with the discharge valve (40) at least at one point. 6. Discharge valve actuating system, as in claim 1, characterized in that the subchamber (70) maintains a permanent fluid communication with the discharge chamber (22) through a connecting intermediate volume (80) , which is dimensioned so as to avoid the instantaneous transfer of pressure from the discharge chamber (22) to the subchamber (70) . 7. Discharge valve actuating system, as in claim 6, characterized in that the connecting intermediate volume (80) includes at least one discharge muffler chamber of the compressor, maintaining a constant fluid communication with the discharge chamber (22) and with the subchamber (70) . 8. Discharge valve actuating system, as in claim 6, characterized in that the subchamber (70) maintains a fluid communication with the connecting intermediate volume (80) , by means of a through channel (24) , provided at least on one of the walls of the discharge chamber (22) . 9. Discharge valve actuating system, as in claim 8, characterized in that the through channel (24) is provided throughout the extension of the valve plate (10) between one end thereof adjacent to the connecting intermediate volume (80) and to the subchamber (70) .

Inventors: LILIE DIETMAR ERICH BERNHARD, LILIE, DIETMAR, ERICH, BERNHARD
Applicants: BRASIL COMPRESSORES SA, LILIE DIETMAR ERICH BERNHARD, EMPRESA BRASILEIRA DE COMPRESSORES S/A - EMBRACO, LILIE, DIETMAR, ERICH, BERNHARD
Application year: 1994
Main classification: F04B39
IPC codes: F04B39